Rotary pulse generators provide one or more digital signals in response to the rotation of a shaft. Typically, a photoelectric or magnetic mechanism attached to the shaft is utilized to produce the signals. For example, in a photoelectric mechanism the shaft is coupled to a disc having alternately clear and opaque pie-shaped segments. A light source is placed on one side of the disc and one or more photosensitive devices are placed on the other side. Pulses are produced as the disc is rotated and the light shines through each clear segment and onto the photosensitive devices.
Rotary pulse generators have been used in instruments to provide incrementing and decrementing of a counter. The resulting value in the counter is then used to control an operation in the instrument. Often, the value in the counter represents a frequency to which a signal is to be tuned.
In various applications where rotary pulse generators are used it is desirable to provide the ability to tune quickly over large areas and to tune slowly and with greater precision when the desired value is approached. Of course, varying the rotational speed of the rotary pulse generator provides some relative difference in tuning speed. However, where an even greater range of tuning speeds is desired, it has been necessary to provide an additional switch to allow selection of coarse, medium and fine tuning rates by the tuning dial.
In accordance with the preferred embodiment of the present invention, each complete revolution of the rotary pulse generator (RPG) produces a predetermined quantity of pulses, e.g., 180 pulses. A divider circuit and a rotational speed sensing circuit produce an output signal by performing a nonlinear division of these pulses dependent on the speed of rotation sensed. For example, at low rotational speeds of the RPG, the pulses received by the divider circuit are divided by 5. Therefore, only 36 pulses are contained in the output signal for each revolution of the RPG. The division decreases in magnitude as the rotational speed increases, until at the higher rotational speeds the divisor is one and 180 pulses are contained in the output signal. In this way a five-to-one increase in tuning speed can be achieved over that possible by simply rotating the shaft at greater rotational speed. Of course, the range of divisors to be used varies with the particular application. In addition, the direction of rotation is sensed to provide a signal to indicate whether incrementing or decrementing is desired.